1. Field of the Invention:
The present invention relates generally to capstan assemblies for rope making machines, and more particularly, to such assemblies having only a single capstan whereby less tensile stress is placed on the advancing rope strand.
2. Description of the Prior Art:
In the manufacture of rope, conventional equipment provides for the supply of plural strands which are fed through equipment that will put a twist into the strands at a constant speed. In accomplishing this, the individual strands are generally directed through a forming die where they are joined and twisted while being drawn through the assembly by metering capstans. In order to assure high quality in the finished product, it is imperative that both the amount of twist and the throughput of rope be maintained constant and be accurately controlled.
Both the twisting of the rope strands and the drawing of the twisted rope through the assembly are controlled by the metering capstans. Metering capstans are similarly used in braided rope making machines which do not twist the rope but draw it directly through a forming die. In both cases, slippage of the rope about the capstans must be avoided.
In prior art rope making assemblies, such as that illustrated in U.S. Pat. No. 3,728,854, two separate capstans have been used with the rope passing around both capstans. The use of two capstans has long been considered to be necessary in order to assure that adjacent windings will not pile up on each other or overlap resulting in binding. While experience has shown that the use of two capstans successfully prevents binding and overlapping, this favorable result has been accompanied by a serious disadvantage in that the tension in the rope windings must be maintained exceptionally high to preclude slipping. Thus, the design of conventional dual-capstan metering assemblies requires that a trade-off be reached between the advantage of eliminated overlapping and the disadvantage of the application of high tensile stresses.
In the early development of rope making machines, several attempts were made to use single capstans. U.S. Pat. No. 317,116, for example, discloses the use of a single capstan which is conically shaped and cooperates with a small, inclined ramp, which acts to prevent the first winding from overlapping. A similar arrangement is illustrated in U.S. Pat. No. 781,281 which again uses a conical capstan to urge the rope by self-slippage toward the reduced diameter and to prevent overlapping. In practice, neither of these approaches has proven to be fully satisfactory since they both necessitate that the rope continually slip higher and higher on the capstan in order to preclude overlapping. In practice, some overlapping does in fact occur, and the slippage makes the throughput rate difficult to accurately control.
Another example of the prior art use of single capstans is U.S. Pat. No. 994,576. In this device, a threaded drum cooperates with a flier assembly to advance the rope or yarn through the apparatus. While the threaded periphery of the drum would at first glance appear to efficiently maintain the windings separate, it is readily apparent that as the drum rotates with respect to the flier, the advancing strand may have to jump from one groove to the adjacent groove.
As the rope making industry progressed from the early machines exemplified by the above-noted patents, it was believed that the dual-capstan arrangement produced superior control and, thus, was a preferred arrangement despite the disadvantage of increased tensile stress. As a result, modern equipment, as illustrated in U.S. Pat. No. 3,728,854, typically incorporates the dual-capstan assembly.